An MIMO (Multi-Input/Multi-Output) communication is attracting attention as a technology for realizing communications of large-volume data such as images in recent years. In the MIMO communication, different items of transmission data (substreams) are transmitted from a plurality of antennas on a transmitting side and the plurality of items of transmission data mixed along a propagation path is separated into the original items of transmission data on a receiving side using a propagation path estimated value (e.g., see FIG. 4 in the Unexamined Japanese Patent Publication No. 2002-44051).
In the MIMO communication, a signal transmitted from a transmission apparatus is actually received by at least the same number of antennas as transmission apparatuses and characteristics of propagation paths between the antennas are estimated based on pilot signals inserted in the signals received by the respective antennas. When, for example, there are two antennas on the transmitting side and two reception antennas, this estimated propagation path characteristic H is expressed by a matrix with 2 rows×2 columns. In the MIMO communication, transmission signals transmitted from the respective transmission antennas are obtained based on an inverse matrix of this propagation path characteristic H and received signals obtained from the respective reception antennas.
Thus, in the MIMO communication, it is possible to separate signals sent from a plurality of transmission antennas at the same timing and same frequency in substream units on the receiving side, and thereby transmit an amount of data proportional to the number of transmission antennas and realize a high-speed, high-volume communication.
However, a reception apparatus which carries out a conventional MIMO communication has a problem that when an interference compensation error occurs due to influences of noise, etc., in a process of separating (compensating for interference) a plurality of items of transmission data, the error rate characteristic of reception data deteriorates. Deterioration of an error rate characteristic of data expected to have higher channel quality than that of other data such as data directed to users having poor channel quality, control information of a communication system or retransmission information in particular has a greater influence on the communication system.
In order to prevent deterioration of the error rate characteristic of reception data due to the interference compensation error, a method of transmitting specific data assigned to only one antenna and a method of transmitting the same data assigned to a plurality of antennas are available. However, using such methods contrarily reduces the transmission rate of the communication system, causing a problem that the data transmission efficiency deteriorates.